Thermophysical characterization and mathematical modeling of convective solar drying of raw olive pomace Abdelghani Koukouch a , Ali Idlimam b,⇑ , Mohamed Asbik a , Brahim Sarh c , Boujemaa Izrar c , Abdellah Bah d , Omar Ansari d a Equipe de Matériaux et Energies Renouvelables, LP2MS, URAC08, Faculté des Sciences, UMI, BP11201, Zitoune, Meknès, Morocco b Equipe de l’Energie Solaire et Plantes Aromatiques et Médicinales, Ecole Normale Supérieure, UCAM, B.P 2400 Marrakech, Morocco c ICARE, CNRS – 1C avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France d LM2PI, ENSET, UM5, Avenue de l’Armée Royale, Madinat Al Irfane, BP 6207 Rabat, Morocco article info Article history: Received 20 January 2014 Accepted 13 April 2015 Keywords: Raw olive pomace Hygroscopic equilibrium Drying kinetics Drying curve characteristic abstract This experimental study is focused on the convective solar drying of raw olive pomace. In this investiga- tion, the desorption/adsorption equilibrium water content of this product has been determined at the drying temperatures of 30 °C, 40 °C and 50 °C, by using the gravimetric static method. Moreover, four mathematical models have been used to predict the hygroscopic behavior of the product during drying process. From a thermodynamic point of view, more significant changes are felt in the thermodynamic properties of natural raw olive pomace in terms of differential enthalpy and entropy of sorption. The characteristic drying curve (CDC) of raw olive pomace has also been experimentally determined. This kinetic measurement is carried out for three temperature values of drying air (45 ± 0.1 °C, 60 ± 0.1 °C and 80 ± 0.1 °C) and also for two values of drying air flow rate D v (0.042 ± 0.002 m 3 s 1 and 0.083 ± 0.002 m 3 s 1 ). The drying rate is empirically determined from the characteristic drying curve, and four mathematical models have been used to describe drying curves. The Midilli–Kucuk model seems to be the appropriate model for drying of the product studied here. Ó 2015 Published by Elsevier Ltd. 1. Introduction In addition to the olive oil, the olive oil industry in the region of Meknes (Morocco) also generates enormous amounts of wastes such as olive pomace. These wastes must be treated and used to avoid their negative impact on the environment. Indeed, energy recovery could respond to different needs in both olive trituration units than in the households of the rural population of this region. This energy conversion is a production of the clean energy based on the olive pomace. Before burning this type of biomass, drying proves to be an unavoidable step. This study falls within the framework of a project called VERA, funded by the ‘‘Region Centre (France)’’ which aims to optimize and validate by experimental testing, an integrated energy recov- ery process by using agricultural wastes as olive pomace. The pre- sent work carries out the first phase of this project which is to prepare agricultural residues (pomace) in particular their drying using solar thermal energy. According to many studies [1,2] which focused on drying of bio- logical products, it has been noted that it is difficult to find a mathematical model governing the temporal evolution of the products during drying. For this reason, only an experimental study allows to determine their drying kinetics. Therefore, it seems useful to study variations of moisture content and those of the dry- ing rate versus time, for different controllable aerothermal param- eters, using an indirect solar dryer operating in forced convection. All the results obtained for a specified product can be gathered into a single curve called ‘‘characteristic drying curve (CDC)’’ whose practical interest is to reduce all the experimental data, so that it can be put in a usable form not only by the experimenter himself, but also by the entire scientific community. On the other hand, good theoretical knowledge of the material hygroscopic character is a key to better understanding the drying process. Indeed, a material is then dried to be used for a particular application usually requires precise water content related to the stability of the product. In fact, within the hygroscopic field in where the bound water and/or water vapor are moving, there is a relationship between the macroscopic equilibrium water content of the product and the surrounding environment. This correlation is nothing other than the sorption isotherm which links the water content, the temperature and the relative humidity of the environ- ment. It characterizes the many interactions between the solid http://dx.doi.org/10.1016/j.enconman.2015.04.044 0196-8904/Ó 2015 Published by Elsevier Ltd. ⇑ Corresponding author. Energy Conversion and Management 99 (2015) 221–230 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman